This invention relates generally to optical inspection systems, and more particularly the invention relates to a stereoscopic electro-optical system for automated inspection of visual displays.
Historically, inspection and alignment of high-precision image-producing displays, such a cathode-ray-tube (CRT), electroluminescent and liquid-crystal flat panel displays, were done by a skilled human operator with the assistance of various optical devices such as microscopes, photometers, overlay grids, and the like. This manual technique is inherently time-consuming and expensive if high quality results are required.
More recently, automated electro-optical systems have been developed to inspect and/or align image-producing displays. While much faster than manual methods, existing inspection systems are not capable of accurately performing inspection of display units-under-test (UUT) as they are delivered to the inspection station by a low-precision assembly line conveyor system, wherein the UUT may be misoriented relative to the inspection system in both angle and distance.
There are several known automated approaches that have been used in the past to make the required inspection and/or alignment. In "fixtured" electro-optical inspection systems, a mechanical fixturing system is used to precisely fix the inspection system relative to the display unit-under-test (UUT) while making the inspection. This method does not have the capability of making rapid inspection and/or alignment of the display UUT on a low-precision assembly line conveyor best, wherein the UUT may be misoriented relative to the inspection system in both angle and distance. In "feature-reference" electro-optical inspection systems, a specific feature which is always found on the UUT is used to compute a correction function which compensates for misalignment in angle and/or distance between the inspection system and the UUT. For example, one commercially available system looks for the bezel (frame) around the cathode-ray-tube display UUT while inspecting these UUTs on a conveyor belt. By assuming the bezel is of a known size and shape, this system deduces the distance and the orientation of the UUT and then generates a correction function for the inspection of the UUT. Unfortunately, this system is undesirably sensitive to minor differences in the size, shape, color, reflectivity and three-dimensional characteristics of the bezel. It is also not as accurate as is desirable for high-accuracy measurements of high-quality display UUTs.
Therefore, a primary purpose of this invention is to provide an electro-optical inspection and/or alignment system that is capable of making rapid measurements and/or electronic alignment of video display units as they are delivered to the inspection station without the necessity for human-handling, fixturing, or otherwise maintaining precise orientation of the display UUT while being relatively insensitive to variations in the angle and distance between the inspection system and the UUT.